Tracked vehicles, that is vehicles whose motion over a surface is imparted by continuous belt-like “tracks” rather than a set of wheels, are known in the art. Vehicles such as earth-movers, tanks and various off-road vehicles can be provided with two or more continuous tracks, also called caterpillar tracks, which provide an increased area of contact between the vehicle and the ground. This increased contact area increases traction and is advantageous in many off-road situations, such as on snow, sand or soft earth. A track can be made of a continuous flexible belt or a plurality of rigid belt elements which are hingedly joined to one another.
It is known to provide tracked vehicles with four or more tracks which can be steered by directing the two front-most tracks, much as a conventional car is steered. It is more common however for tracked vehicles to comprise a single pair of tracks, one extending along either side of the vehicle. Such vehicles can be steered by varying the speed of one of the two tracks. To turn to the left, the right track is accelerated and/or the left track is decelerated. It is therefore known to provide the driver independent control of each track in order to enable turning. Typically, this independent control is enabled by having a motor drive a hydraulic pump, which in turn independently powers left and right side hydraulic motors.
However, because the market for such tracked vehicles is relatively small, it is also known to provide attachments or kits for adapting a conventional tractor to run on tracks. Such an attachment conveniently allows the use of a wheeled vehicle in the summer and a tracked vehicle in the winter.
However, conventional tractors typically comprise a pair of steered front wheels and a pair of driven rear wheels whose motive power comes from a motor through a transmission and a differential. When adapting such a tractor to run on tracks, the driven rear wheels are typically replaced with sprocket wheels which are used to drive the tracks. This arrangement is well suited for driving the tractor forwards or backwards, but conventional tractors do not typically provide independent control of the speed of the rear wheels. Various steering systems have been proposed to for conventional tractors adapted to run on tracks.
U.S. Pat. No. 5,343,960, issued Sep. 6, 1994 to Sylvain Gilbert, describes an attachment for converting a rear wheel drive tractor into a tracked snow grooming vehicle. A snow plow is mounted to the rear of the tractor and the converted tractor is steered by hydraulically actuating the coupling between the tractor and the trailing snow plow so as to control the orientation of the plow and thereby induce turning.
U.S. Pat. No. 3,710,886, issued Jan. 16, 1973 describes a mechanism for converting a wheeled vehicle into a tracked vehicle wherein the steering is accomplished by controlling the braking of the tracks in order to steer the vehicle.
Also known in the art are U.S. Pat. Nos. 1,665,470, 1,810,138, 2,356,931, 3,976,153, 4,448,273 4,821,824 and 4,865,141 which describe different continuous track devices for providing track propulsion for a vehicle.
However, it would be advantageous to provide an improved steering system for vehicles propelled by endless tracks which could operate in a more efficient manner than existing system. In particular, it would be advantageous to provide a steering system which varies the speed of the tracks in order to steer without employing the braking system, which represents an undesirable loss of motive power. It would also be advantageous to provide such a steering system which could be used to convert a rear wheel driven wheeled vehicle to a tracked vehicle.